1. Field of the Invention.
This invention relates to agricultural irrigation and more particularly to the movement and roll ahead device of a vehicle to move irrigation pipe with sprinklers thereon.
2. Description of the Prior Art
Agricultural irrigation systems normally operate upon soft level ground and, therefore, normally there is not a problem of them rolling ahead. However, anytime the irrigation pipe is empty, there is a problem of the wind blowing it ahead. Although this problem is particularly acute with side roll systems requiring special preventative measures, (e.g., WATTS U.S. Pat. No. 3,618,859), the problem also exists with center pivot systems.
Trojan bar or ratchet driven center pivot systems having pawl drives and pawl detents are well known, (e.g., ZYBACK U.S. Pat. No. 2,604,359 and GORDON U.S. Pat. No. 2,893,643).
When the system is driven by a rotating electric motor such as BOYCE U.S. Pat. No. 2,711,615, the problem is controlled by the fact that these motors normally use a worm drive and the worm drive itself operates as a roll ahead device.
LUNDVALL ET AL, U.S. Pat. No. 3,766,937, sought a solution to the problem of roll ahead, which is usually a downhill problem, where each vehicle has two driven lugged wheels. His solution was to have detent bar, the length of which was the distance from the rim of one wheel to the rim of the next less the lug height. The lugs on the two wheels were offset from one another and the detent bar was moved from the rim of one wheel back to the rim of the other wheel, permitting a lug on the wheel having the detent bar removed from it to go forward while the detent on the opposite wheel prevented it from rolling ahead.